1. Field of the Invention
This invention relates to a transmitting method, a receiving method, a communication method, and a bi-directional bus system, which are used in a system in which devices, e.g., a television image receiver or a video tape recorder, etc. are connected to each other by using a bi-directional bus to control, from other devices, sub-devices, e.g., a monitor image receiver, a TV tuner, or a video deck, etc. included in the devices.
2. Description of the Related Art
In recent years, there have been popularly used systems in which a plurality of audio equipments or visual equipments (hereinafter referred to as AV equipments) are connected by means of video signal lines or audio sinal lines (hereinafter referred to as AV signal lines).
In such AV systems, equipments are connected by means of a system control bus (hereinafter simply referred to as a bi-directional bus) in addition to the above-described AV signal lines to control respective equipments. In a practical sense, Audio, Video and audiovisual systems Domestic Digital Bus (hereinafter referred to as D2B) standardized by the so-called publication 1030 of IEC, a Home Bus System (hereinafter referred to as HBS) standardized by the ET-2101 of EIAJ, and the like are known. Through the bi-directional bus, other devices are controlled from equipments (devices), e.g., a television image receiver, a video tape recorder, and a video deck player (hereinafter respectively referred to as TV, VTR, VDP), etc., or sub-devices, e.g., a monitor image receiver (TV monitor), a TV tuner, a video deck, or an amplifier, etc. included in other devices are controlled from devices.
Namely, communication from a sub-device included in a device to a sub-device included in any other device (hereinafter referred to as communication from sub-device to sub-device), communication from a sub-device included in a device to any other device (hereinafter referred to communication from sub-device to device), communication from a device to a sub-device included in any other device (hereinafter communication from device to sub-device), and communication from a device to any other device are carried out through a bi-directional bus. In other words, communications are carried out through a plurality of routes (paths).
The format of a transmit signal used in a bi-directional bus as described above, e.g., D2B will now be described. In D2B, control commands for controlling a sub-device of destination, etc. and/or data indicating the operating state, etc. are caused to have a frame configuration as shown in FIG. 1, and are transmitted through the bi-directional bus.
Namely, one frame consists of a header field 101 for specifying the header indicating the leading portion of the frame, a master address field 102 for specifying a source device address, a slave address field 103 for specifying a destination device address, a control field 104 for specifying control bits indicating communication, etc, in the state where a destination device is in a lock state, or in non-lock state, and a data field 105 for specifying control commands or data,
The header of the header field 101 consists of, as shown in FIG. 2, a start bit 101a of one bit for providing synchronization, and mode bits 101b for prescribing a transmission speed (rate) or the number of bytes of the data field 106. These mode bits 101b are 1.about.3 bits. At present, three modes of mode 0 where the data field 105 is comprised of 2 bytes at the maximum, mode 1 where the data field 105 is comprised of 32 bytes at the maximum (16 bytes at the maximum in the case of communication from slave to master), and mode 2 where the data field 105 is comprised of 128 bytes at the maximum (64 bytes at the maximum in the case of communication from slave to master) are prescribed.
The source device address of the master address field 102 consists of, as shown in the above-mentioned FIG. 2, master address bits 102a of 12 bits for specifying a source device address, and a parity bit 102b of 1 bit.
The destination device address of the slave address field 103 consists of, as shown in the above-mentioned FIG. 2, a slave address bits 103a of 12 bits for specifying a destination device address, a parity bit 103b of 1 bit, and an acknowledge bit 103c of 1 bit for sending acknowledge from the destination device.
The content of the control field 104 consists of, as shown in the above-mentioned FIG. 2, control bits 104a comprised of 4 bits indicating the direction of the control command, or indicating the lock state or the non-lock state, a parity bit 104b of 1 bit, and an acknowledge bit 104c of 1 bit.
In the data field 105, as shown in the above-mentioned FIG. 2, data bits 105a of 8 bits, end of data bit 105b of 1 bit and parity bit 105c of 1 bit are repeated as occasion demands. Assuming now that data bits 105a are assumed to be data #1, #2, #3, . . . in order from the beginning, e.g., Operation code (hereinafter referred to as OPC) "Begin 2" (i.e., code "BD"h (h represents hexadecimal notation)) indicating communication relating to sub-device, OPC "Begin 1" ("BC" h) indicating communication through HBS, and OPC "Begin 0" ("BB"h) indicating communication through other bus, etc. are assigned (allocated) to data #1. Further, Operand (hereinafter referred to as OPR) with respect to these OPCs are assigned to data #2.
OPR with respect to these OPCs, e.g., OPR with respect to OPC "begin 2" consists of, as shown in FIG. 3, bits b.sub.5, b.sub.4, b.sub.3, b.sub.2 (b.sub.7 is the Most Signicant Bit (MSB) for identifying service codes of the Communication Telephony (CT) system, the Audio Video and Control (AV/C) system, and the Housekeeping (HK) system, etc.; and bits b.sub.1, b.sub.0 indicating any one of communication from sub-device to sub-device, communication from sub-device to device, communication from device to sub-device, and communication from device to device, viz., indicating presence or absence of Source Sub-Device Address (hereinafter referred to as SSDA) or Designation Sub-Device Address (hereinafter referred to as DSDA). It is to be noted that bit b.sub.7 is caused to be always zero, and bit b.sub.6 is reserved for future standardization and is caused to be 1 at present. In more practical sense, b.sub.1 =0, b.sub.0 =0 indicates communication from sub-device to sub-device; b.sub.1 =0, b.sub.0 =1 indicates communication from sub-device to device; b.sub.1 =1, b.sub.0 =0 indicates communication from device to sub-device; and b.sub.1 =1, b.sub.0 =1 indicates communication from device to device.
Accordingly, e.g., in the communication from a sub-device of a TV (device) to a video deck (sub-device) of a VTR (other device), as shown in FIG. 4A, an address of TV is assigned as master address bits to the master address field 102; an address of VTR is assigned as slave address bits to the slave address field 103; and a code "A"h indicating write of a control command, e.g., from master to slave is assigned to the control field 104. Further, OPC "Begin 2" is assigned to data #1; e.g., code "54"h indicating communication from sub-device to sub-device is assigned to data #2 as OPR for OPC "Begin 2"; an address of a sub-device of TV is assigned to data #3 as SSDA; and an address of a sub-device of VTR is assigned to data #4 as DSDA. To the subsequent data #5, e.g., control command for playing (reproducing) the video deck of VTR is assigned.
Further, e.g., in the communication from sub-device of TV to VTR (device), as shown in 4B, address of TV, address of VTR and code "A"h indicating write of control command from master to slave are respectively assigned to the master address field 102.about.the control field 104, Further, OPC "Begin 2" is assigned to data #1, code "55"h indicating communication from sub-device to device is assigned to data #2, and address of sub-device of TV is assigned to data #3 as SSDA. Further, control command is assigned to data #4, Namely, in this case, since there is no destination sub-device, assignment of DSDA is unnecessary,
Further, e.g., in the communication from TV (device) to sub-device of VTR, as shown in FIG. 4C, address of TV, address of VTR and code "A"h indicating write of control command from master to slave are respectively assigned to the master address field 102.about.the control field 104. Further, OPC "Begin 2" is assigned to data #1, code "56"h indicating communication from device to sub-device is assigned to data #2, and an address of sub-device of VTR is assigned to data #3 as DSDA. In addition, control command is assigned to data #4. Namely, in this case, since there is no source sub-device, assignment of SSDA is unnecessary.
In addition, e.g., in the communication from TV (device) to VTR (device), as shown in FIG. 4D, address of TV, address of VTR, and code "A"h indicating write of the control command from master to slave are respectively assigned to the master field 102.about.the control field 104. Since there is no communication relating to the sub-device, control command is assigned to data #1. Namely, assignments of OPC "Begin 2", SSDA and DSDA are unnecessary.
The control command will now be described. The number of codes that can be represented by 8 bits is 256. However, with 256 kinds of codes, it is not sufficient to carry out control of the entirety of the AV equipment. In view of this, in HBS or D2B, a command Table comprised of OPC and OPR shown in FIG. 5 is used.
Namely, the command Table consists of OPC of 1 byte indicating the name of a controlled system, and OPR of 1 byte or plural bytes indicating the control content. General commands commonly used for respective equipments are assigned to code "AO"h.about.code "BF"h of OPC, a group of function commands are assigned to code "CO"h.about.code "DF"h, and a group of special function commands are assigned to code "EO"h.about.code "FF"h. In this case, code "80"h.about.code "9F"h are reserved.
In more practical sense, control commands such as video commands, audio commands, deck/player commands or tuner commands, etc. share, e.g., the area of the function command group (code "CO"h.about.code "DF"h). For example, code "CO"h indicates control of contrast in the case of the video command, control of volume in the case of the audio command, repeat in the case of the deck/player command, and control of band in the case of the tuner command.
Further, control commands such as video camera commands or timer commands, etc. share, e.g., the area of the special function command group (code "EO"h.about.code "FF"h). For example, code "EO"h indicates control of zoom in the video camera command, and year in the case of timer command.
On the other hand, so called ASCTII code, controlling value code and alias code are assigned to code "20"h.about.code "5F"h of OPR, and standard OPR is assigned to code "60"h.about.code "7F"h. In this case, code "OO"h.about.code "1F"h are reserved.
In more practical sense, e.g., standard OPR (code "60"h.about.code "7F"h) has common meanings every control commands such as video commands or audio commands described above. For example, code "60"h means ON, code "70"h means OFF, code "63"h means decrement, and code "73"h means increment.
Meanwhile, in HBS, Table Selector (TS) (i.e., general command in which OPC consists of code "B9"h) is placed before the control command to prescribe correspondence relationship between OPC of the control command and the function command or the special function command. In D2B, command Table is selected in terms of default value by DSDA specified by OPC "Begin 2". In actual terms, e.g., in DSDA, video command is selected in TV monitor (sub-device), audio command is selected in audio amplifier, deck/player command is selected in video deck, video player, audio deck and CD player, and tuner command is selected in TV tuner and audio tuner.
As described above, in the conventional communication method of D2B, etc., the position of OPC of the control command varies, e.g., in dependency upon the position of data #5, data #4, data #4, data #1 of data field 105 and communication form (kinds of communication routes (paths)). Therefore, it is required for device or sub-device on the receiving side to specify the position of OPC prior to carrying out decode of OPC of the control command. For this reason, there was the problem that hardware or software becomes complicated. In addition, also in forming a transmit signal and transmitting such signal, the position of OPC of the control command varies depending upon communication route, resulting in the problem that software, etc. becomes complicated.